The present invention relates to a system for generating a signal.
Sensors are being used increasingly to control or regulate the processes in motor vehicles. However, this means that ever more sensor signals must be transmitted independently of one another to the control or regulating units. In so doing, the individual signals must meet various requirements. If the individual signals are combined to form a xe2x80x9ccomposite signalxe2x80x9d, the individual requirements must be retained.
It is known to measure the speeds of the vehicle wheels in order to control or regulate the braking force, motive force and/or the dynamics of vehicular operation of a motor vehicle. A great variety of methods (e.g., Hall or magnetoresistive sensors) are set forth for this purpose in the related art. It is also known to ascertain the wear and tear of the brake lining of a vehicle brake by, for example, embedding contact pins at a certain depth of the brake linings, the contact pins triggering a contact when the brake lining is worn away to this depth.
So, for example, the article xe2x80x9cIntegrierte Hall-Effekt-Sensoren zur Positions-und Drehzahlerkennungxe2x80x9d (Integrated Hall-Effect Sensors for Detecting Position and Speed), Electronic Industry 7-1995, pp. 29 through 31 describes active sensors for use in the motor vehicle for anti-lock braking, traction, engine and transmission control and regulating systems. In a two-wire configuration, such sensors supply two current levels which are converted in an appropriate control unit into two voltage levels by a measuring resistor.
In addition to the Hall-effect sensors mentioned, the use of magnetoresistive sensors for detecting speed is also known, for example, from the article Neue, alternative Lxc3x6sungen fxc3xcr Drehzahlsensoren im Kraftfahrzeug auf magnetoresistiver Basisxe2x80x9d(New, Alternative Design Approaches for Speed Sensors in the Motor Vehicle on a Magnetoresistive Basis), VDI Reports No. 509,1984.
U.S. Pat. No. 4,076,330 describes a special joint arrangement for determining the wear of a brake lining and for detecting the wheel speed. To that end, the ascertained brake-lining wear and the wheel speed, detected by an inductively operating sensor, are conducted via a joint signal line to an evaluation unit. This is achieved in that, in reaction to a detected brake-lining wear, the wheel-speed sensor is completely or partially short-circuited.
Other systems as are described, for example, in German Patent No. 43 22 440, need at least two signal lines between a wheel unit and the evaluation unit for determining the speed and the brake-lining wear at a wheel and a wheel brake, respectively.
In the case of the aforesaid speed detection, it is known that the air gap between the rotating ring gear and the actual sensor element has a considerable influence on the quality of the speed signal. Reference is made, for example, to German Patent No. 32 01 811 on this matter.
Furthermore, for example, for help when starting from rest (so-called Hillholder), information is needed about the direction of rotation of the wheels. In this case, information as to whether the vehicle is moving backwards is particularly necessary. Reference is made, for example, to German Patent No. 35 10 651 concerning this.
The above-mentioned information, as well as further information or additional information (for example, brake-lining wear, air gap, direction of rotation) is generally ascertained close to the wheel and evaluated in a control unit disposed at a distance from the wheel. To that end, the information must be transmitted to the control unit.
In the case of an engine (internal combustion engine and/or electromotor), it is known to ascertain the engine speed using inductive, magnetoresistive or Hall sensors.
The German Published Patent Application No. 196 09 062 describes superimposing the information of an analog speed signal, that periodically has two specifiable current or voltage levels, with the digital information with regard to the brake-lining wear, the air gap and/or the direction of rotation, such that the current or voltage levels of the analog speed signal are changed in coded manner. The increase in the current levels for transmitting the additional digital information has the advantage that only a two-wire connection is necessary between the sensor unit and the control unit. However, in addition to an increase in power loss, the elevated current levels lead to an increased voltage drop at the measuring resistor in the control unit. It may be that the change of the voltage levels does not increase the power loss, but it makes a three-wire connection (voltage supply, ground, signal line) necessary between the sensor unit and the control unit.
An object of the present invention is to superimpose the speed information and the additional information as simply and reliably as possible.
The present invention is based on a system for generating a signal which, in addition to first information representing the rotational speed of a rotating part, contains at least second information. The signal changes over time between a first and a second current level and/or voltage level (high/low).
The crux of the present invention is that the first information is represented by the time interval between a substantially identical change either between the first to the second level (high/low edge) or a substantially identical change between the second to the first level (low/high edge). On the other hand, the second information is represented by the length of time either of the first or of the second level.
Compared to the related art mentioned in the introductory description, the present invention has the advantage that no further current levels or voltage levels are necessary to transmit the additional information. Furthermore, the additional information can be evaluated relatively simply, since only the length of time either of the first or of the second level, thus the pulse width, has to be measured for this purpose. The present invention also offers the possibility of attaining high data integrity by pulses which are as long as possible.
In one particularly advantageous embodiment, the system of the present invention is used in a motor vehicle. The first information represents the speed of a vehicle wheel, the speed of a vehicle engine designed as a gasoline engine, diesel engine and/or electromotor, and/or the speed of a shaft functionally coupled to the vehicle transmission. The second information includes at least one information component, the information components representing
the distance between the rotating part and a sensor element detecting the rotational speed, and/or
the brake-lining wear at at least one vehicle wheel brake, and/or
the direction of rotation (DR) of the rotating part, and/or
the fitting position (EL) of a sensor element detecting the rotational speed.
In particularly advantageous manner, different priorities are assigned to the information components to be transmitted by the signal, such that in response to the presence of the information component having the highest priority, the other information components are not transmitted. This ensures that the most important information is reliably transmitted.
According to the present invention, the speed information is transmitted by the time intervals between the substantially identical changes (high/low edge or low/high edge). In a particularly advantageous refinement of the present invention, the signal is generated in such a way that, prior in time to these essentially identical changes (high/low edge or low/high edge) which are important for the speed information, the current level and/or voltage level (high/low) which the signal has prior to these changes is set for at least one specifiable time duration. The setting according to the present invention of a level prior to the actual change (xe2x80x9cadvance bitxe2x80x9d), which is to be evaluated for the speed information, assures the reliable transmission of the speed signal in every case.
This setting of a level prior to the actual change (xe2x80x9cadvance bitxe2x80x9d) can be carried out in that a trigger signal is generated and, in reaction to the generation of the trigger signal, the signal is set to the first or second current level and/or voltage level (high/low). In doing this, provision is made in particular that the trigger signal is generated as a function of the rotational speed of the rotating part.
Another refinement of the present invention provides that, when the rotating part is stationary, the signal is generated in such a way that it has the first or second current level and/or voltage level (high/low) for a specifiably fixed time duration. This makes it possible to recognize the standstill of the rotating part. Furthermore, this also makes it possible to check the proper functioning of the sensor element and the transmission lines.
A further refinement of the present invention describes an advantageous embodiment of the evaluation of the signal generated according to the present invention. For this evaluation, from the signal generated according to the present invention, first of all a speed quantity representing the rotational speed of the rotating part is ascertained from the time interval between a (substantially identical) change either between the first to the second level (high/low edge) or a (substantially identical) change between the second to the first level (low/high edge). This speed quantity is compared to at least one threshold value. The evaluation of the length of time either of the first or of the second level for ascertaining the second information is then carried out as a function of the comparison result. Thus, the rotational speed of the rotating part is advantageously taken into account during the evaluation of the second information. In this context, it can be provided that, given the presence of higher speed quantities, only parts of the second information are evaluated. This ensures that only that second information is evaluated which can be reliably transmitted.
It is particularly provided that the information components having the highest priority are evaluated up to higher speed quantities as the information components having lower priority.